Nonaqueous electrolyte secondary batteries, particularly lithium secondary batteries, have a high energy density and are thus in wide use as batteries for, for example, personal computers, mobile telephones, and portable information terminals. Such nonaqueous electrolyte secondary batteries have recently been developed as on-vehicle batteries.
As a nonaqueous electrolyte secondary battery such as a lithium-ion secondary battery, known is a nonaqueous electrolyte secondary battery that includes a porous film as disclosed in, for example, Patent Literature 1, which porous film contains polyolefin as a main component.